The photovoltaic effect is well known and widely used in the conversion of radiant energy to electricity. Present photovoltaic devices are generally constructed as large area planar semiconducting P-N junctions that receive illumination at incidence normal to the plane of the junction. Individual photocells can produce large currents under intense illumination, but only at low voltage, typically 65% of the band-gap of the semiconductor. Losses due to resistance are significant in such devices, as are losses due to undesirable low energy photon absorption in the high field region of the planar junction.